https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119959
Bug ID: 119959
Summary: [15 regression] simple loop miscompiled into an
endless loop
Product: gcc
Version: 15.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c
Assignee: unassigned at gcc dot gnu.org
Reporter: bruno at clisp dot org
Target Milestone: ---
Created attachment 61205
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=61205&action=edit
test case foo.c
gcc 15.1.0 (built from source, full bootstrap, with isl) generates wrong code
for the function 'rehash_symtab' in the attached test case foo.c.
How to reproduce:
$ gcc -Wall -O1 -S -fno-dwarf2-cfi-asm foo.c -o foo.gcc15.O1.s
For comparison, gcc 14.2.0 (also built from source, full bootstrap, with isl)
generates correct code:
$ gcc -Wall -O1 -S -fno-dwarf2-cfi-asm foo.c -o foo.gcc14.O1.s
In the source code, the function rehash_symtab contains two loops, each with a
call to newinsert() in the middle, and a final epilogue that stores two words
in memory and then returns.
In foo.gcc14.O1.s (correct) you can see the second loop like this:
===============================================================
.L8:
addq $8, %r12
cmpq %r12, %rbx
je .L16
.L9:
movq STACK(%rip), %rax
movq -24(%rax), %rdx
movq 10(%r12,%rdx), %rdi
cmpq $symbol_tab_data+6, %rdi
je .L8
movq %rdi, %rdx
andl $7, %edx
cmpq $2, %rdx
je .L8
movq %rdi, (%rax)
addq $8, STACK(%rip)
movl %ebp, %esi
call newinsert
subq $8, STACK(%rip)
jmp .L8
===============================================================
In foo.gcc15.O1.s (miscompiled) you can see the second loop like this:
===============================================================
.L7:
addq $8, %rbx
.L8:
movq STACK(%rip), %rax
movq -24(%rax), %rdx
movq 10(%rbx,%rdx), %rdi
cmpq $symbol_tab_data+6, %rdi
je .L7
movq %rdi, %rdx
andl $7, %edx
cmpq $2, %rdx
je .L7
movq %rdi, (%rax)
addq $8, STACK(%rip)
movl %ebp, %esi
call newinsert
subq $8, STACK(%rip)
jmp .L7
===============================================================
You can see that here,
- between .L7 and .L8 the loop termination condition is missing,
(foo.c line 118),
- accordingly the loop has become and endless loop,
- and as a consequence the function's epilogue has been removed.
